Modern integrated circuits, IC, consume more and more power at lower supply voltages. Therefore, the traditional approach of delivering converted power from a power supply unit (PSU) at the right voltage to the IC on a printed circuit board (PCB) via a connector on the PCB is no longer a viable solution. This can easily be understood by simple calculations using ohms law: an IC with a supply voltage of 2.2 V and a power consumption of 30 W requires a current of approximately 13 A. A PSU with such ratings exhibits large ohmic losses due to the resistance of the leads from the PSU to the IC.
A common solution to this problem is to place the PSU close to the IC on the PCB and to utilize an intermediate bus voltage provided to the PSU on the PCB via a connector. It is also common today to integrate a power controller on the PCB that controls all PSU's with a dedicated bus, such as a PMBUS for example.
This results in PCB's comprising several intertwined subsystems related to different functions of the circuit. One critical subsystem is the power supply system. The power supply system must provide large power consumers, such as a field programmable gate array (FPGA) circuit, with stable power at low supply voltage and high current. Especially the phase of turning on a FPGA circuit proves to be very demanding for the PSU since it is usually recommended to ramp-up the supply voltage in a controlled manner.
During the development of a modern PCB it is frequently desired to test each subsystem separately before integrating the full system on the PCB. Hence, in order to test the PSU system on the PCB an electronic load is needed to replace the current consuming subcircuits such as the FPGA circuit.
Such an electronic load is commonly available as bench-top equipment and rack mounted devices connected to the PCB by means of leads and connectors.
Another aspect to test is the effect of the environment on the PCB, and especially temperature effects on the stability and functionality of the power supply system on the PCB.
This environmental test is usually performed in an environmental test chamber, see FIG. 1. Such an environmental test is performed by placing the PCB in the chamber with the electric load connected to the power supply system. The temperature in the chamber is gradually increased until the desired working temperature is reached. Then the electrical test of the power supply system is performed by turning on the power supply system and variate the electrical load to simulate different working conditions.
Some problems exists with this setup. First, the environmental test chamber is usually quite expensive and bulky. Secondly, the leads connecting the electronic load to the PCB are usually long and cause parasitic inductances and capacitances between the electronic load and the PCB. Such parasitic effects makes it difficult to correctly simulate slew-rate effects on the PCB by means of the electronic load.